An example of a welding monitoring apparatus for monitoring whether or not the actual welding condition values are within the appropriate range corresponding welding condition command values in the prior art is disclosed in Japanese Laid-Open Patent No. 4-237565. That is, as shown in FIG. 13, the apparatus comprises a CPU circuit 100 and an external interface circuit 101. A printer 103 is connected to the CPU unit through a printing output interface 102. A measurement and display changeover circuit 104 is used as a measurement and display changeover means, and a limiter upper and lower limit selection adjusting circuit 105, a limiter upper and lower limit adjuster 106, and a limiter selector 107 are combined to comprise a limiter upper and lower limit setting means. Actual welding conditions are obtained through a welding current detector 108 and a welding voltage detector 109, and are displayed in a display unit 110.
In this configuration, limiter levels of the upper and lower limits can be directly set by the limiter upper and lower limit setting means, and an output result, as shown in FIG. 14, is printed out so that the welding current and the welding voltage are monitored to determine whether or not they are within an appropriate range. In FIG. 14, in the second line, UL=230 A (amperes) and LL=210 A indicate the upper and lower limits of the present welding current monitoring range. The asterisked "1UL" in FIG. 14 indicates the monitoring of the welding current, showing that it is lower than the lower limit level at 208 &lt;indicated by "a" mark and higher than the upper limit level at 233&gt; indicated by "b" mark.
However, in such a welding monitoring apparatus, since the upper and lower limits (allowable) of the welding current and welding voltage, as the objects of welding quality control are specified by actual numeric values, if the welding condition command is changed during operation, the upper and lower limits of the welding current and welding voltage as the objects of welding quality control cannot be used unless they are set again in actual numeric values, accordingly. Moreover, since an unstable arc section right after an initial arc start in one welding section is also monitored, a detection error may occur although the weld is not defective.
Moreover, crater treatment is executed at the end of one welding section, but during this crater treatment operation, since the welding condition command is lowered by about 50 A in welding current and 5V in welding voltage from the actual welding conditions, a detection error occurred in this crater treatment section in the prior art.
In an automatic welding line by a robot, etc., when used in the conventional arc welding condition monitoring apparatus, operation information or other information of the robot at a moment of welding failure could not be obtained, and it took time to plan a countermeasure or to understand the welding failure tendency, and as a result, prompt measures could not be put into effect.
In the light of the problems of the prior art, it is hence an object of the invention to present a control apparatus of an arc welding robot, using a teaching playback robot, capable of monitoring whether the arc welding conditions are within an appropriate range or not, presenting to a user the information showing at which teaching point during robot operation is the point of occurrence if an arc welding condition goes out of the appropriate range, and maintaining and controlling the arc welding quality sufficiently, inexpensively, easily and promptly.
Concerning the prior art technology for treating the crater properly at the end of welding, if the arc is cut off immediately at the end of welding, generally, the deposit metal is thin in this area, the crater is formed on a bead appearance and the appearance is impaired and as a result, the welding strength is decreased. Accordingly, the welding operator builds up the weld metal at the end of welding, which is called crater treatment. With the welding robot, crater treatment is done by a user's teaching, and the art for saving this teaching step is disclosed in Japanese Laid-Open Patent No. 8-39241. In short, the current, the voltage and a crater filler time for crater treatment are preliminarily stored, and crater treatment is executed at the arc cut-off point according to the second current, voltage and crater filler time, and then the arc cut-off command is executed.
Usually, the welding power source commands and controls a wire feed device 16 for feeding consumable electrodes (hereinafter called wires) so that a wire feed speed may be proportional to the welding current command value. However, there is a response delay of hundreds of milliseconds from the issue of a command for a new wire feed speed from the welding power source to the wire feeder reaches the commanded new wire feed speed.
Accordingly, if the response delay time necessary for changing the wire feed speed remains unknown, it is not known whether the crater welding condition command is executed at the time of actual crater welding treatment, and a lot oftime is spent determining the welding condition. Herein, at the end point of welding, if the time difference of the robot control apparatus sending a crater welding condition command and an arc cut-off command to the welding power source are far smaller values than the delay time corresponding to the response delay of the wire feeder mentioned above, wherein the wire feed speed is the same as in the regular welding condition command value, and the welding condition command value is a far smaller crater welding condition command value than the regular welding condition command value, and when welding in such a condition, the wire is fused and sticks to the work at the end of welding, and so-called wire stick (fusion of wire on object of welding) occurs. If wire stick occurs, the operator must cut of the stuck wire with snippers or the like, and polish the bead surface, and this post-treatment hinders unmanned operation by robot and impairs the cycle time.
To avoid this wire stick in crater treatment, the wire feed amount should be less than the wire melting allowable value, and when the welding condition command value is changed, it is known that wire stick does not occur if enough response delay time of the wire feeder is provided by the portion corresponding to the changing amount.
The invention is devised in the light of the above problems of the prior art, and it is hence and object thereof to execute crater treatment appropriately in the control apparatus of the arc welding robot, to judge whether or not necessary time is maintained until the wire reaches the command feed speed after transmission of the crater welding condition command (welding current, welding voltage, welding end command (arc cut-off, welding shield gas cut-off, etc.)) to the welding power source, to execute the welding condition command value when maintained, or to execute the crater treatment without changing the wire feed speed, if not maintained, at the same regular welding condition command value by ignoring the crater welding condition command value, thereby preventing wire stick and enhancing cycle time and promoting automation of the automatic welding line using a robot.